A refrigerator is provided with a valve drive device which distributes a common refrigerant (fluid) to a plurality of compartments for cooling the respective compartments. The valve drive device includes a valve seat plate 13′ through which an inflow port 13c and outflow ports 13a, 13b for the refrigerant penetrate in its thickness direction, a sealing case (not shown) which covers the front face side of the valve seat plate 13′, and a valve element (not shown) which slides on the front face of the valve seat plate 13′ to open or close the outflow ports 13a, 13b as shown in FIGS. 5(A) and 5(B). Further, a rotor support shaft 18 and a valve element support shaft 35 are fixed in the valve seat plate 13.
The inflow port 13c and the outflow ports 13a, 13b in the valve seat plate 13′ are formed in a stepped hole whose front face side is formed with a small diameter and whose rear face side is formed with a large diameter. The large diameter portion on the rear face side of the inflow port 13c and the outflow ports 13a, 13b is used as a pipe insert hole and the inflow pipe 28c and the outflow pipes 28a, 28b are brazed to the pipe insert holes in the state where their tip ends are respectively abut with the stepped portions of the stepped holes.
In the valve drive device constructed as described above, the area of the surface of the valve seat plate 13′ where the outflow ports 13a, 13b are formed becomes a sliding face for the valve element and thus a high degree of surface accuracy is required to completely cut off the refrigerant. Also, it is required for the valve seat plate 13′ to be sufficiently thick such that distortion does not occur in the sliding face for the valve element even when the valve seat plate 13′ is heated to a temperature caused by brazing, for example, the temperature of 1000° C. or more at the time when the pipes 28a, 28b, 28c are fixed by brazing. In addition, the valve seat plate 13′ is made of iron system material so as to be capable of being brazed and a SUS material is used because of its corrosion resistance.
Therefore, in the case that the valve seat plate 13′ is conventionally produced, cutting work (lathe work) is required to perform on a thick SUS member and thus the valve seat plate 13′ becomes expensive.
It is conceivable that the valve seat plate is produced by using a method of forging instead of cutting work, but forging also causes the valve seat plate to be expensive. In addition, a high degree of dimensional accuracy and positional accuracy of hole is difficult to obtain by forging. Also, residual stress becomes large in the case of forging and thus, when brazing is performed, a face where a high degree of accuracy is required is distorted by heat due to the brazing.
Further, it is also conceivable that the valve seat plate is produced by using a method of sintering and molding instead of cutting work, but sintering and molding also causes the valve seat plate to be expensive although it is not more than cutting work. Moreover, sealing treatment is required to a sintered body but, in the case of resin impregnation which is a general sealing treatment, resin cannot endure a high temperature at the time of brazing. In addition, since the surface hardness of a sintered body is low, tolerance to sliding of a valve element is low. Further, since the smallest dimension of the diameter of a hole which can be formed by sintering is limited, a cutting work is required as a secondary working to form a hole, for example, with the diameter of 1.50.